Field of the Invention
The invention relates to systems of transmitting data, particularly of a technical nature, from a rotary part to a non-rotary part of a vehicle. These may be data relating to physical parameters, including parameters such as pressure, temperature, friction, and wear. The invention relates more particularly to wheel units, safety inserts, and the aerials of these systems and their installation on vehicle wheels.
For example, the invention may be used with a safety system intended to warn the driver of a vehicle of the condition of tires of the vehicle, such as loss of pressure in one of the tires of the vehicle.
WO 94/20 317 and U.S. Pat. No. 5,600,301 disclose a system comprising, for each wheel, a wheel unit with at least one pressure sensor, power supply means, a high-frequency transmitter and an aerial. As shown in FIG. 2 of WO 94/20 317, this wheel unit is fixed to the wheel valve. Such fixing may entail problems during assembly and dismantling of the tires on the wheels, particularly if the valve hole is not disposed in the external side of the rim well, such as in, for example, the wheel disclosed in patent EP 701 911. In this system, it is necessary to follow a specific assembly/dismantling procedure in order to take into account the presence of the wheel unit, as any inattention may lead to damage to or destruction of the units.
U.S. Pat. No. 5,285,189 discloses a system having wheel units fixed to the radially outer wall of the rim wells of the wheels by a fixing collar. This type of fixing limits the problems encountered during assembly of the tires on their wheels. However, it has been found that the unit can pivot when the vehicle is moving. Their position is therefore not known when the tires are dismantled and here too, any inattention can lead to damage to or destruction of the units. Additionally, the units are disposed immediately next to the metal wall of the rims of the wheels. This environment makes the reliability of radio transmissions between the wheel units and the central receiving and processing units disposed in the chassis of the vehicles difficult.
The patent EP 0 775 601 discloses a safety system for wheels equipped with safety inserts having wheel units disposed inside the volume of the safety insert. It has been found with such a system that there may still be difficulties in the output of radio transmissions, particularly in certain positions of the wheel unit for radio transmission relative to the vehicle chassis.